Switch mods to per-folder auto-discovery and resourcepack to single zip

- PackDefinition: replace mods[]/resourcepacks[] with modsFolder (string) + resourcepackPath (string); drop PackAsset
- Editor: replace dynamic add/remove lists with two single inputs; remove the now-dead JS for adding/removing rows
- Server: expose GET /file/mods/<folder>/index.json that returns the list of .jar names; folder name restricted to [a-zA-Z0-9_-]+
- Installer: fetch the listing JSON and download each jar from /file/mods/<folder>/<file>.jar; download the single resourcepack from /file/resourcepacks/<file>.zip directly into resourcepacks/

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

src/server/app.ts

@@ -1,6 +1,7 @@
 import express from 'express'
 import session from 'express-session'
 import path from 'node:path'
+import fsp from 'node:fs/promises'
 import { manifestRootPath, manifestDirPath, fileDirPath, viewsDirPath, publicDirPath } from '../shared/paths'
 import { indexRouter } from './routes/index'
 import { opRouter } from './routes/op'
@@ -69,6 +70,30 @@ app.use((req, res, next) => {
   next()
 })
 
+// 모드 폴더 안의 .jar 파일 목록을 JSON으로 반환. 설치기가 자동 다운로드용으로 사용.
+app.get('/file/mods/:folder/index.json', async (req, res) => {
+  const folder = req.params.folder
+  if (!/^[a-zA-Z0-9_\-]+$/.test(folder)) {
+    res.status(404).json({ files: [] })
+    return
+  }
+  const dir = path.join(fileDirPath, 'mods', folder)
+  try {
+    const entries = await fsp.readdir(dir)
+    const files = entries
+      .filter((name) => /\.jar$/i.test(name))
+      .filter((name) => !name.includes('/') && !name.includes('\\'))
+      .sort()
+    res.json({ files })
+  } catch (error) {
+    if ((error as NodeJS.ErrnoException).code === 'ENOENT') {
+      res.status(404).json({ files: [] })
+      return
+    }
+    throw error
+  }
+})
+
 app.use('/file', express.static(fileDirPath, { fallthrough: true, index: false }))
 
 app.use('/', indexRouter)